Ransomware is one of the biggest problems on the web right now. It's a form of malicious software -- malware -- which encrypts documents on a PC or even across a network. Victims can often only regain access to their encrypted files and PCs by paying a ransom to the criminals behind it.

A ransomware infection often starts with someone clicking on what looks like an innocent attachment, and it can be a headache for companies of all sizes if vital files and documents (think spreadsheets and invoices) are suddenly encrypted and inaccessible. But that's not the only way to get infected.

Cybercriminals didn't use to be so obvious. If hackers infiltrated your corporate network, they would do everything possible to avoid detection. It was in their best interests not to alert a victim that they'd fallen victim to a cyber criminal.

Known as AIDS or the PC Cyborg Trojan, the virus was sent to victims -- mostly in the healthcare industry -- on a floppy disc. The ransomware counted the number of times the PC was booted: once it hit 90, it encrypted the machine and the files on it and demanded the user 'renew their license' with 'PC Cyborg Corporation ' by sending $189 or $378 to a post office box in Panama.

The AIDS demand for payment - by post.

Image: Sophos

How did ransomware evolve?

This early ransomware was a relatively simple construct, using basic cryptography which mostly just changed the names of files, making it relatively easy to overcome.

But it set off a new branch of computer crime, which slowly but surely grew in reach -- and really took off in the internet age. Before they began using advanced cryptography to target corporate networks, hackers were targeting general internet users with basic ransomware.

One of the most successful variants was 'Police ransomware', which tried to extort victims by claiming to be law enforcement and locking the screen with a ransom note warning the user they'd committed illegal online activity, which could get them sent to jail.

However, if the victim paid a fine, the 'police' would let the infringement slide and restore access to the computer by handing over the decryption key. Of course, this wasn't anything to do with law enforcement -- this was criminals exploiting innocent people.

An example of 'Police ransomware' threatening a UK user.

Image: Sophos

While somewhat successful, these forms of ransomware often simply overlaid their 'warning' message on the user's display -- and rebooting the machine could get rid of the problem and restore access to files which were never really encrypted.

Criminals learned from this and now the majority of ransomware schemes use advanced cryptography to truly lock down an infected PC and the files on it.

What are the main types of ransomware?

Ransomware is always evolving, with new variants continually appearing in the wild and posing new threats to businesses. However, there are certain types of ransomware which have been much more successful than others.

Locky remained successful because those behind it regularly update the code with changes which allow it to avoid detection. They even update it with new functions, including the ability to make ransom demands in 30 languages, helping criminals more easily target victims in around the world. Locky became so successful, it rose to become most prevalent forms of malware in its own right.

Cryptowall is another form of ransomware which has found great success for a prolonged period of time. Starting life as doppleganger of Cryptolocker, it's gone onto become one of the most successful types of ransomware.

While some ransomware developers -- like those behind Locky or Cryptowall -- closely guard their product, keeping it solely for their own use, others happily distribute ransomware to any wannabe hacker keen to cash in on cyber extortion - and it's proved to be a very successful method for wide distribution.

One of the most common forms of ransomware distributed in this way is Cerber, which has been known to infect hundreds of thousands of users in just a single month. The original creators of Cerber are selling it on the dark web, allowing other criminals to use the code in return for receiving 40 percent of each ransom paid.

This particular family of ransomware is constantly evolving, with its developers regularly adding new features to ensure its continued success. Indeed, the cryptography behind Cerber is so advanced that there's currently no decryption tools available to help those infected with the latest versions.

In the biggest ransomware attack to date, WannaCry - also known as WannaCrypt - also known as WannaCry and Wcry - caused chaos across the globe in an attack which started on Friday 12th May 2017.

Wannacrypt ransomware demands $300 in Bitcoin for unlocking encrypted files - a price which doubles after three days. Users are also threatened, via a ransom note on the screen, with having all their files permanently deleted if the ransom isn't paid within a week.

Of all the countries hit by the attack, it was Russia which was hit the hardest according to security researchers, with the WannaCry malware crashing Russian banks, telephone operators and even IT systems supporting transport infrastructure. China was also hit hard by the attack, with 29,000 organisations in total falling victim to this particularly vicious form of ransomware.

Other high-profile targets included the car manufacturer Renault which was forced to halt production lines in several locations as the ransomware played havoc with systems.

What all the targets had in common is that they were running unsupported versions of Microsoft Windows, including Windows XP, Windows 8 and Windows Server 2003.

This cyberattack first hit targets in Ukraine, including its central bank, main international airport and even the Chernobyl nuclear facility before quickly spreading around the globe, infecting organisations across Europe, Russia, the United States and even Australia.

After some initial confusion as to what this malware was - some said it was Petya, some said it was something else - researchers at Bitdefender came to the conclusion suggest that this outbreak is down to a modified version of Petya ransomware, combining elements of GoldenEye - a particularly vicious relative of Petya - and WannaCry ransomware into extremely potent malware.

Petya ransom note

Image: Symantec

Yes, this second form of ransomware also exploits the same EternalBlue Windows exploit which provided WannaCry with the worm-like features to spread through networks (not simply through an email attachment as is often the case) and hit 300,000 computers around the world - except Petya/NotPetya/GoldenEye is a much more vicious attack.

The attackers ask for a Bitcoin ransom of $300 to be sent to a specific email address - which has now been shut down by the email service - host, but the the way this very sophisticated ransomware apparently was equipped with very basic, non-automated functions for accepting ransoms has lead some to suggest money isn't the goal.

Ultimately, whatever the size of the company, time is money and the longer your network is down because of malware, the more it's going to cost your business.

Even if you regain access to your encrypted documents by paying a ransom, there will be additional costs on top of that. In order to avoid future attacks -- especially if you've been marked as an easy target -- be prepared to invest in additional cybersecurity software and to pay for additional staff training.

There's also the risk of customers losing trust in your business because of poor cybersecurity and taking their custom elsewhere.

Why should businesses worry about ransomware?

To put it simply: ransomware could ruin your business. Being locked out of your own files by malware for even just a day will impact on your revenue. But given that ransomware takes most victims offline for at least a week, or sometimes months, the losses can be significant. Systems go offline for so long not just because ransomware locks the system, but because of all the effort required to clean up and restore the networks.

And it isn't just the immediate financial hit of ransomware which will damage a business; consumers become wary of giving their data to organisations they believe to be insecure.

How does ransomware infect your PC?

It's the modern enterprise's reliance on the internet which is enabling ransomware to boom. Everyday, every employee receives hundreds of emails and many roles require these employees to download and open attachments, so it's something which is often done on autopilot. Taking advantage of employees' willingness to open attachments from unknown senders is allowing cybercriminals to successfully run ransomware campaigns.

A spam email claiming the target has purchased a flight - complete with fake invoice containing the ransomware.

Image: Symantec

While some messages give away clues to their malicious nature with poorly-worded messages or strange return addresses, others are specially tailored to look as convincing as possible, and appear no different from any other message the victim might be sent.

Once the malicious attachment has been opened, the user is encouraged to enable macros in order to view and edit the document. It's when this is enabled that the ransomware code hidden within the macros strikes. It can encrypt files in seconds, leaving the victim with a ransom note demanding a payment ranging from a few hundred dollars to tens of thousands of dollars in order to get them back.

But it's not just email attachments you need to worry about: one recent malvertising campaign managed to infect PCs with ransomware without users even clicking on the malicious adverts: visiting the compromised website was enough to be infected because the hackers deploying the Astrum exploit kit to leverage an old Flash exploit according to a security firm.

Which organisations are targets for ransomware?

Any business can find itself a victim of ransomware, but perhaps the most high-profile incident occurred when the Hollywood Presbyterian Medical Center in Los Angeles became infected with Locky ransomware. The malware infection left doctors and nurses unable to access patient files for days, until the hospital opted to give into the ransom demands of hackers in order to restore services.

"The quickest and most efficient way to restore our systems and administrative functions was to pay the ransom and obtain the decryption key," Allen Stefanek, CEO of the hospital, said at the time.

Locky is one of the most successful forms of ransomware.

Image: F-Secure

Hospitals and other healthcare organisations are popular targets for ransomware attacks, because they are often willing to pay. Losing access to data is a life-or-death matter for them -- and hospitals don't want to be held responsible for letting people die due to poor cybersecurity. However, there are even cybercriminals who think attacking hospitals is too despicable an activity.

Small and medium-sized businesses are a popular target because they tend to have poorer cybersecurity than large organisations. Despite that, many SMEs falsely believe they're too small to be targeted -- but even a 'smaller' ransom of a few hundred dollars is still highly profitable for cybercriminals.

Why is ransomwareso successful?

You could say there's one key reason why ransomware has boomed: because it works. Organisations can have the best antivirus software in the world, but all it takes for ransomware to infect the network is for one user to slip up and launch a malicious email attachment and discover all their files have been encrypted.

If organisations weren't giving in to ransom demands, criminals would stop using ransomware. But businesses do need access to data in order to function so many are willing to pay a ransom and get it over and done with.

Meanwhile, for criminals it's a very easy way to make money. Why spend time and effort developing complex code or generating fake credit cards from stolen bank details if ransomware can result in instant payments of hundreds or even thousands of dollars from large swathes of infected victims at once?

There are even ransomware-as-a-service schemes available on the dark web which allow the most technically inept wannabe cybercriminals to start sending out ransomware -- in exchange for a percentage of their ill-gotten gains going directly into the pockets of the creators of the malware, of course.

What does Bitcoin have to do with the rise of ransomware?

The rise of crypocurrencies like Bitcoin has made it easy for cybercriminals to secretly receive payments extorted with this type of malware, without the risk of the authorities being able to identify the perpetrators. The secure, untraceable method of making payments -- victims are asked to make a payment to a bitcoin address -- makes it the perfect currency for criminals who want their financial activities to remain hidden.

Cybercriminal gangs are becoming more professional -- some even offer customer service and help for victims who don't know how to acquire or send Bitcoin, because what's the point of making ransom demands if users don't know how to pay? Some organisations have even hoarded some of the crypto-currency in case they get infected and their files encrypted and have to pay in Bitcoin in a hurry.

Globe3 ransom demand for 3 Bitcoin - including a 'how to ' guide for those who don't know how to buy it

On a technical level, stopping employees from being able to enable macros is a big step towards ensuring that they can't unwittingly run a ransomware file. Microsoft Office 2016 -- and now Microsoft 2013 -- both carry features which allow macros to be disabled. At the very least, employers should invest in anti-virus software and keep it up-to date, so that it can warn users about potentially malicious files. Backing up important files and making sure those files can't be compromised during an attack in another key.

How long does it take to recover from a ransomware attack?

Simply put, ransomware can cripple a whole organisation - an encrypted network is more or less useless and not much can be done until systems are restored.

If your organisation is sensible and has backups in place, systems can be back online in the time it takes the network to be restored to functionality, although depending on the size of the company, that could range from a few hours to days.

However, while it's possible to regain functionality in the short term, it can be the case that organisations struggle to get all systems back up and running - as demonstrated by the Petya attack.

Outside of the immediate impact ransomware can have on a network, it can result in an ongoing financial hit. Any time offline is bad for a business as it ultimately means the organisation can't provide the service it sets out to - and can't make money - but the longer the system is offline, the bigger that can be.

That's if your customers want to do business with you; in some sectors, the fact you've fallen victim to a cyberattack could potentially drive customers away.

Initially launching as a portal offered portal offers decryption tools four for familities of ransomware - Shade, Rannoh, Rakhn, and CoinVault - the scheme is regularly adding more decryption tools for even more versions of ransomware including Crypt XXX, MarsJoke, Teslacrypt, Wildfire and Nemucod.

The portal - which also contains information and advice on avoiding falling victim to ransomware in the first place - is updated as often as possible in an effort to ensure tools are available to fight the latest forms of ransomware.

For example, another decryption tool was recently released which may be able to help if your PC has been hit by one of the original versions of the Petya malware -- the so-called Red Petya, Green Petya, and GoldenEye -- and may enable you to recover the lost files (although it can't help with PetrWrap or those hit by the Petya/NotPetya global attack). However, these tools don't always work so it is always wise to make additional backups.

Another way of working around a ransomware infection is to ensure your organisation regularly backs up data offline. It might take some time to transfer the backup files onto a new machine, but if a computer is infected and you have backups, it's possible just to isolate that unit then get on with your business. Just make sure that crypto-locking crooks aren't able to encrypt your back-ups too.

But be warned: if word gets out that your organisation is an easy target for cybercriminals because it paid a ransom, you could find yourself in the crosshairs of other cybercriminals who are looking to take advantage of your weak security. And remember that you're dealing with criminals here and their very nature means they may not keep their word: there's no guarantee you'll ever get the decryption key, even if they have it. Decryption isn't even always possible: there are stories of victims making ransom payments and still not having encrypted files unlocked.

For example a type of ransomware targeting Linux discovered earlier this year demanded a Bitcoin payment but did not store encryption keys locally or through a command-and-control server, making paying the ransom futile at best.

As ransomware continues to evolve, it's therefore crucial for your employees to understand the threat it poses, and for organisations to do everything possible to avoid infection, because ransomware can be crippling and decryption is not always an option.